Heat milk and butter in a small saucepan over medium low heat until butter is melted. Let cool about 5 minutes (if mixture is steaming, it's too hot) until 120-130°F.
In a large bowl, or the bowl of a stand mixer fitted with a dough hook, combine 2 cups flour, Red Star Yeast Platinum Instant Sourdough, salt, and sugar.
Add warm milk mixture and eggs and mix until it forms a wet dough.
Add remaining flour 1/4 cup at a time while kneading on medium low speed until dough clears the sides of the bowl but still sticks slightly at the bottom. It should feel tacky to the touch. You may not need all 4 cups of the flour.
Continue to knead as needed until dough is smooth and elastic, and when pulled it should stretch for several inches before breaking. If it breaks sooner, keep kneading.
Cover bowl with plastic wrap and place somewhere warm to rise until doubled, about 1 hour.
Gently punch down the dough and reshape into a ball. Let rest for about 10 minutes